The present invention relates to a device and method for ensuring safe and qualitative use of a wet on wet textile printer and, more particularly, but not exclusively to a method and apparatus that prevents chemical effects of the wetting agent that occur in the presence of inks not specially designed for the wetting agent, or for chemical reactions between the wetting agent and the wrong kind of ink.
The present embodiments relate to a method and apparatus of preventing health hazards to an operator or others in the vicinity of wet printing of textiles, or damage to the printed garment or damage to equipment.
Digital printing on garments or textiles in general, is performed by very small droplets containing miniscule amounts of colorant. To obtain an image with acceptable intensity the ink drops should not be permitted to enter the bulk of fabric but rather should display all the colorant at the fabric's surface.
Many existing digital printers use pretreatment procedures which generate an impregnated layer on the surface of the fabric and print the image on the layer. This is the wet on dry process, and the layer prevents the ink drops from being absorbed into the fabric.
Wet on dry generally prevents the ink from penetrating into the textiles so that the present issue does not arise.
Generally this is conceived by applying an under layer or base layer by spraying the substrate with suitable solution, and drying or more usually heat pressing, that result in a uniform planar base which may accept and immobilize the jetted ink droplets of the digital printing.
Wet on wet printing however not only allows the ink to enter the fabric but indeed the wetting composition may enable free flow and mix of the inks on the substrate, thus exacerbating the problem. The wet on wet printing of the present applicants is described, for example, in International Patent Publication Nos. WO 2005/076730 and WO 2005/15089, and also in International Patent Application No. PCT/IL2010/000645, filed Aug. 10, 2010.
In order to ensure that the colorant remains at the fabric surface it is therefore necessary to pretreat the fabric prior to printing. Substrate preparation by treatment is needed to produce a high quality image on the garment or textile.
The pretreatment may be performed by applying ink immobilizing solution, that reacts instantaneously with the digital ink droplets, thus preventing the ink drop from being absorbed into the fabric to disappear, or from bleeding or feathering into adjacent ink droplets. Using immobilizing solution, the image is immediately printed and stabilized upon the wet surface and may subsequently be thermally dried and cured.
The solution used for wetting in the preprinting treatment, which may include ink immobilizing solution, may be chemically active and may react with inks that were not specifically designed to be used with the solution. Such reactions may give rise to discharge of unreacted reagents and be a danger to persons in the vicinity and/or such reactions may cause damages to the fabrics being printed.
A consequence of this is that unless specific inks are used, which can neutralize the major part of the hazardous ingredient in the spray solution during the immobilization process, use of wet on wet printing is not safe.
Besides an application of the immobilizing solution by external sprinkler, the ink immobilizing solution may be supplied to the fabric through a printhead such as an inkjet print head. Supply of the ink immobilizing solution may be simultaneous with the printing or may precede the printing, and the use of a print head allows for precise placement of the immobilizing solution in relation to the region to be printed.
Furthermore there are often workplace requirements and safety regulations that set maximum exposure levels for many substances. It is therefore necessary for anyone installing wet on wet printing equipment to keep traces of regulated materials that reach the operator below the allowed exposure levels (TWA-STEL).
One way of avoiding exceeding the permitted levels of the regulated components in the pretreatment solution regulated components, is to provide neutralizing components in the inks that neutralize the regulated components.
Suitable ink formulations are therefore designed with neutralizing components in such a way that when applied on the pretreatment solution, significant components of the droplet immobilizing materials of the pretreatment solution are neutralized, thus keeping their concentration in air under the limit levels.
As described in International Patent Publication No. WO 2005/15089 and International Patent Application No. PCT/IL2010/000645, the ink immobilization is effected by instantaneous restriction of flowability of liquid ink components containing the pigments after the droplet hits the substrate, thus preventing bleeding or feathering.
The colorant immobilization can be performed by, for example, a volatile organic acid, which may form a part of the wetting composition. The acid reacts with a compatible component in the jetted ink to thereby affect congelation of the ink, thus also ensures that the concentration of the acid does not exceed the TWA-STEL values.
Another issue that arises when inks other than the specifically designed inks are used, is preventing damage to the equipment. Such damage may include corrosion and blockage of print heads, which may occur as a result of introduction of incompatible inks into the printer. Print heads are a relatively expensive part of the printing apparatus and it is desirable to avoid the expensive printheads from being blocked.
Another issue that arises from use of inks not designed to be used with the wetting composition is protection of the garments to be printed from damage and being ruined.
Inks that lack wet on wet immobilization features may furthermore be diluted by the solution and the adjacent drops may therefore bleed one into another. Thus the resulting image is of reduced or very low quality, and the garment may be destroyed.